Electron temperature fluctuations in drift-resistive ballooning turbulence

Three-dimensional nonlinear simulations of collisional plasma turbulence are presented to model the behavior of the edge region of tokamak discharges. Previous work is extended by including electron temperature fluctuations ${\mathrm{T̃}}_e.$ The basic paradigm that turbulence and transport are controlled by resistive ballooning modes in low temperature plasma and nonlinearly driven drift wave turbulence in higher temperature regimes persists in the new system. Parallel thermal conduction strongly suppresses the ability of the electron temperature gradient ${\mathrm{\nabla T}}_e$ to drive the turbulence and transport everywhere except the very low temperature edge of the resistive ballooning regime. As a consequence, over most of the resistive ballooning regime only the density gradient drives the turbulence and the temperature fluctuations are convected as a passive scalar. In the drift wave regime only the density gradient acts to drive the nonlinear instability and the temperature fluctuations have a relatively strong stabilizing influence on the turbulence due to an enhanced damping of density and potential fluctuations resulting from local electron heating.